1. Field of the Invention
The present invention relates to in-line type electron guns and color picture tube apparatuses using the same. More particularly, the invention relates to a color picture tube apparatus used in television receivers, computer displays and the like, and an in-line type electron gun used therefor provided with a focusing electrode and a final accelerating electrode that form a main lens.
2. Description of the Related Art
In order to obtain a high-resolution image on the phosphor screen of a color picture tube apparatus, it is necessary to decrease the spot diameters on the phosphor screen of three electron beams corresponding respectively to the colors R (red), G (green) and B (blue) emitted from an electron gun, to make the shapes of the spots be a perfect circle, and to simultaneously achieve a just focus of the three electron beams at a common focus voltage on the phosphor screen. In addition, at the time of assembling the electron gun, it is necessary to perform precise positioning of three electron beam passage apertures formed in each of the electrodes of the electron gun.
As a conventional electron gun, the electron gun disclosed in Japanese Patent No. 3056515 is known, for example. In the electron gun disclosed in this patent, a focusing electrode and a final accelerating electrode that form a main lens are disposed at a predetermined gap. A single oval-shaped aperture having a major axis in the horizontal direction is provided on the focusing electrode on its end face opposed to the final accelerating electrode. A field forming electrode composed metal plate is provided on the focusing electrode in a position set back from the aperture, and three electron beam passage apertures disposed in an in-line arrangement in the horizontal direction are formed in the field forming electrode. A single oval-shaped aperture having a major axis in the horizontal direction also is provided on the final accelerating electrode, on its end face opposed to the focusing electrode. A field forming electrode is provided also on the final accelerating electrode in a position set back from the aperture, and three electron beam passage apertures disposed in an in-line arrangement in the horizontal direction are formed in the field forming electrode.
The three electron beam passage apertures formed in the field forming electrode of the conventional electron gun have the following shape. That is, as shown in FIG. 11, a central electron beam passage aperture 101b is formed in an oval or ellipse shape having a major axis in the vertical direction. The outer halves of electron beam passage apertures 101a and 101c provided on both sides of the electron beam passage aperture 101b (the electron beam passage aperture 101c on the right side is not shown) are each formed in the shape of a semicircle. When the in-line direction is an X-axis direction, the direction perpendicular to the in-line direction is a Y-axis direction and the center of the electron beam passage apertures 101a and 101c is X=0 and Y=0, the inner halves of the electron beam passage apertures 101a and 101c are each formed in a shape encircled by a curve represented by the equation Xn+Yn=Rn (where R is a constant), and n is more than 2.0 and not more than 3.0. Additionally, in FIG. 11, numeral 100 denotes the field forming electrode. It should be noted that FIG. 11 depicts the outlines of the inner half of the electron beam passage aperture 101a when n is 2.0, 2.15, 2.25 and 2.5.
As described above, by disposing the field forming electrode 100, in which the three electron beam passage apertures 101a, 101b and 101c are formed, away from the end faces of the focusing electrode and the final accelerating electrode, each of the three main lens fields overlaps with the adjacent main lens field. This enlarges the effective lens diameter of the main lens, thereby making it possible to decrease the beam spot diameter on the phosphor screen. Additionally, the upper and lower arcs of the inner halves of the side electron beam passage apertures 101a and 101c are bulged outward, and optimum focusing conditions can be attained in the horizontal and vertical directions by appropriately selecting the value of n, as with the case where the apertures are vertically elongated. Accordingly, it is possible to make the shapes of the spots of the side electron beams formed on the phosphor screen to be close to a perfect circle. Moreover, as with the case where the shapes of the apertures are a perfect circle, the side electron beam passage apertures 101a and 101c have a shape in which their diameters in the horizontal direction and those in the vertical direction are equal and the upper and lower arcs of the inner halves thereof are bulged outward, so that conventional regulating pins having a circular cross section can be passed through the side electron beam passage apertures 101a and 101c. In this case, the side electron beam passage apertures 101a and 101c are in contact with the regulating pins on the whole area of the arcs of the outer halves and at the central point (the intersection point with the horizontal axis) of the inner halves, making it possible to perform center alignment with high precision.
However, in the above-described conventional electron gun, the field forming electrode in the focusing electrode or in the final accelerating electrode is located in a position set back from the opposing end face of the final accelerating electrode or of the focusing electrode. Accordingly, it is not possible to make a central main lens field and the side main lens fields, among three main lens fields acting respectively on the three electron beams, to have the same intensity. This results in a problem of not being able to simultaneously achieve a just focus of the three electron beams on the phosphor screen.
In addition, there has been a problem that among the beam spots formed on the phosphor screen as a result of focusing and converging the three electron beams, the central beam cannot be formed in the shape of a perfect circle, although the side beams can.
The present invention was achieved in order to solve the above-described problems in the prior art, and it is an object of the present invention to provide an in-line type electron gun that is capable of making a central main lens field and the side main lens fields, among three main lens fields acting respectively on three electron beams, have the same intensity, as well as being capable of making the shape of even the spot of the central electron beam formed on a phosphor screen be close to a perfect circle, even when a field forming electrode in a focusing electrode or in a final accelerating electrode is disposed away from the opposing end face of the final accelerating electrode or of the focusing electrode to increase the effective lens diameter of the main lens. It is another object of the present invention to provide a color picture tube apparatus using the above-described in-line type electron gun.
In order to solve the above-described problems, a structure of the in-line type electron gun according to the present invention comprises: a focusing electrode and a final accelerating electrode that form a main lens and that are disposed at a predetermined gap. The focusing electrode has a first aperture in an end face thereof on the final accelerating electrode side and houses a first field forming electrode in a position set back from the first aperture. The final accelerating electrode has a second aperture in an end face thereof on the focusing electrode side and houses a second field forming electrode in a position set back from the second aperture.
Each of the first and the second field forming electrode is provided with a central electron beam passage aperture and an aperture or a notch disposed on each side of the central electron beam passage aperture and having a half-arc shaped portion protruding towards the central electron beam passage aperture that are disposed in an in-line arrangement.
When a direction of the in-line is an X-axis direction, a direction perpendicular to the direction of the in-line is a Y-axis direction and the center of the central electron beam passage aperture is X=0 and Y=0, the central electron beam passage aperture of at least one of the focusing electrode and the final accelerating electrode has a shape that passes through intersection points of the X-axis and the Y-axis with a curve represented by an equation (X/R1)2+(Y/R2)2=1 (where R1 and R2 are constants) and that has an area smaller than an area encircled by the curve.
With this structure of the in-line type electron gun, even when the first field forming electrode in the focusing electrode or the second field forming electrode in the final accelerating electrode is disposed away from the opposing end face of the final accelerating electrode or of the focusing electrode to increase the effective lens diameter of the main lens, it is possible to make a central main lens field and the side main lens fields, among three main lens fields acting respectively on three electron beams, have the same intensity. This simultaneously achieves a just focus of the three electron beams on the phosphor screen. Moreover, it is possible to make the shape of the spot of the central electron beam, as well as the shapes of the spots of the side electron beams, each formed on the phosphor screen, be close to a perfect circle.
In the above-described structure of the in-line type electron gun of the present invention, it is preferable that the central electron beam passage aperture has a shape encircled by a curve represented by an equation (X/R1)n+(X/R2)n=1, where n is more than 1.5 and less than 2.0. According to this preferable example, it is possible to decrease the difference in intensity between a central main lens field and the side main lens fields, among three main lens fields acting respectively on the three electron beams, by optimizing the value of n in the range of 1.5 less than n less than 2.0. Consequently, it is possible to achieve simultaneously a just focus of the three electron beams on the phosphor screen, even when a single focus voltage common to the three electron beams is applied to the focusing electrode and the final accelerating electrode. Furthermore, the use of this structure makes it possible to make the shape of the spot of the central electron beam formed on the phosphor screen be close to a perfect circle. In this case, it is preferable that n=about 1.90 to about 1.95.
In the above-described structure of the in-line type electron gun of the present invention, it is preferable that a relationship R1 less than R2 is satisfied. According to this preferable example, it is possible to readily make the lens effects in the horizontal and vertical directions equal by canceling the main lens field in which the lens effect in the horizontal direction is weaker than that in the vertical direction by the main lens field in which the lens effect in the horizontal direction is stronger than that in the vertical direction, thereby making the shape of the spot of the central beam formed on the phosphor screen be a perfect circle.
In the above-described structure of the in-line type electron gun of the present invention, it is preferable that a cylindrical intermediate electrode is further provided between the focusing electrode and the final accelerating electrode. According to this preferable example, it is possible to expand the main lens field in the axis direction of the electron gun by adjusting the electric potential of the intermediate electrode to an arbitrary electric potential between the electric potentials of the focusing electrode and the final accelerating electrode, thereby further increasing the effective lens diameter of the main lens. Consequently, it is possible to further decrease the beam spot diameter on the phosphor screen, achieving an even higher resolution of a color picture tube apparatus.
A structure of the color picture tube apparatus of the present invention comprises:
a bulb comprising a face panel having a phosphor screen including phosphors of a plurality of colors on an inner surface thereof and a funnel connected to a rear portion of the face panel;
an electron gun housed in a neck portion of the funnel;
a shadow mask having a plurality of electron beam passage apertures for passing an electron beam emitted from the electron gun and being disposed in a predetermined position in the bulb with a predetermined gap kept from the phosphor screen; and
a deflection yoke mounted at a circumference of the funnel on the neck portion side,
wherein the above-described in-line type electron gun of the present invention is used as the electron gun.
This structure of the color picture tube apparatus uses the above-described in-line type electron gun of the present invention as the in-line type electron gun, so that it is possible to decrease the spot diameters of three electron beams corresponding respectively to the colors R (red), G (green) and B (blue) emitted from the electron gun, on the phosphor screen, while making the shapes of the spots be a perfect circle, and to simultaneously achieve a just focus of the three electron beams at a common focus voltage on the phosphor screen. This makes it possible to obtain a color picture tube of a high resolution.